In many fields, the efficient detection and quantification of particles depends on the ability first to deposit those particles on a planar substrate. Consider, for example, the challenge of detecting and quantifying the contents of a drop of whole blood under a microscope. Whole blood contains various types of particles (e.g., different kinds of blood cells) suspended in serum. If a drop of blood were viewed under a microscope without first making an effort to spread the blood cells apart from each other, the blood cells would appear as overlapping images under the microscope, making them difficult to count, identify, or study individually. Accordingly, it is important to separate the blood cells from each other before studying them, such as by distributing them across the surface of a planar substrate, e.g., a glass microscope slide. In some fields, the efficient detection and quantification of particles further depends on the ability to deposit the particles on the substrate in a desired arrangement, e.g., in a two-dimensional pattern, to a uniform height, in a monolayer, in relatively close proximity to one other, or some combination of the foregoing.
One field that depends on the ability first to deposit particles on planar substrates before analyzing the particles is “cellular astronomy.” Cellular astronomy is known and described in the art. See, e.g., Howard M. Shapiro, Cellular Astronomy—A Foreseeable Future in Cytometry, 60A CYTOMETRY PART A 115-124 (2004). Briefly, and in one aspect, cellular astronomy can achieve the systematic examination of very large numbers of cells by first spreading the cells over the surfaces of one or more substrates, and by then using imaging technology to systematically examine the cells. Typically, an imager starts by simultaneously examining cells visible within a field of view, and continues by moving the field of view across the substrate, continuing region by region until the desired portion of the substrate has been imaged.
One important application of cellular astronomy is the detection and quantification of cell types present in a mixture of cells. For example, in the treatment and management of cancer, it is useful to know whether circulating tumor cells (“CTCs”) are present among other cells in the blood. Because CTCs are known to occur in very low concentrations, for example 1 CTC per 1,000,000,000 blood cells, it is necessary to inspect a very large number of cells in order to determine with confidence whether or not CTCs are present. In order to ensure that cells are examined and accurately identified, it is desirable that they be spread in a monolayer. In order to decrease the number of regions that must be studied and thereby speed the process, it is further desirable that cells be spaced relatively closely together.
Although many technologies, such as cellular astronomy, rely on the ability to deposit particles on planar substrates in a desired two-dimensional pattern, existing methods for depositing particles on substrates are limited in their scope, utility, or versatility. Accordingly, there exists a need for new and improved methods and systems for quickly and efficiently depositing particles, such as cells, onto a flat surface in a desired arrangement, allowing the particles to be studied.